Everything goes well as I progress through the game... I walk down Hell, I reach Cybie...
And when I kill Cybie and the game gives me the message that I have defeated him, the game crashes and saves my game right on Cybie's level, and I don't have the ammo I used to kill him.
I had a nuke with me, so I whipped it out and used it to see if it was just an ocassional bug. The nuke killed Cybie and me, indeed, but when it said that I had destroyed him, the same error occured again!
Then, it saved my game, once again. I loaded it again, and this time let Cybie kill me without putting a fight, and in my mortem, it says I sacrificed myself to destroy the Cyberdemon. What the hell, game?